1. Field of the Invention
This invention relates to a planetarium and, more particularly, to an improved planet projection system for a planetarium.
2. Description of Related Art
Conventional schemes for a planet projection system to drive each of sleeve-type planet projectors for reproducing and projecting the movement of planets, i.e. the inconstant velocity elliptic motion (Keplerian motion) of planets, include: a mechanical scheme in which an annual driving shaft is associated with each of sleeve-type planet projectors through a gear train for driving them; a modeling control scheme in which a driving apparatus operates a gear train for controlling a planet projection system, which is a receiver, by control signals transmitted from an apparatus for reproducing the inconstant velocity elliptic motion (Keplerian motion) (e.g., Japanese Patent Publication No. 37-3218); and a computer scheme in which each of sleeve-type planet projectors is driven in a biaxially control on the basis of calculated values (e.g., Japanese Patent Laid-open No. 60-39675, Japanese Patent Laid-open No. 60-230682).
In the mechanical and modeling control schemes of such schemes in prior art, the planet projector is continuously driven through the gear train to reproduce the movement of planets. Accordingly, for the projection of a travel position of a planet at a desired time in the past or future, the gear train must be rotated by turns corresponding to a time period from the time of the present position of the target planet to the required time. For example, the moving for one hundred years might take as much as 30 minutes. Further, the use of gears does not allow the smooth moving of each planet projector, which may cause a wobbly projected image and noise. Still further, because a revolution period of a planet is not an integer number, the use of the gear train imposes a limitation on the reproduction of planets. Reproducing the movement of the planets within a range of a long time period involves the inevitable problem of the occurrence of cumulative error.
In the latter computer scheme, since the sleeve-type planet projector is biaxially controlled by using the X- and Y-axes intersecting at right angles, assuming that a plurality of planet projectors are provided, it is difficult to provide a vertical arrangement of the planet projectors on a fixed star projection globe. Because of this, as disclosed in the aforementioned Japanese Patent Laid-open No. 60-230682, the planet projection system must be located at a distance from the fixed star projection globe. This leads to a reduction in the number of seats due to the installation space of the planet projection system, and also to the eclipse of light flux emitted from the planet projector. Further, since a main computer calculates the signals for driving the planet projector, trouble occurring in the main produces a problem of the impossibility of the planet projection.
It is an object of the present invention to provide a planetarium having a planet projection system overcoming the aforementioned problems associated with the prior art.
The present invention provides a planetarium comprising a fixed star projection globe, a main computer and a planet projection system. The planet projection system comprises: a rotatable stage rotatably mounted on a fixed shaft, positioned concentrically with a precession axis of the fixed star projection globe or positioned in proximity and parallel to the precession axis, to perform an X-axis motion; at least one sleeve-type planet projector positioned at an eccentric position with respect to an X axis on the rotatable stage and provided for a Y-axis motion for allowing a projection direction to vary upward and downward in relation to the rotatable stage; and a planet-movement operation unit for receiving date and time data from the main computer and controlling the X-axis motion and the Y-axis motion on the basis of the received date and time data.
The present invention configured as described above has the unique effects described below.
1) The rotatable stage is rotatably mounted on the fixed shaft, positioned concentrically with the precession axis of the fixed star projection globe or positioned in proximity and parallel to the precession axis, to achieve an X-axis motion. The sleeve-type planet projector is mounted on such a rotatable stage. This configuration. allows the planet projection system to operate in synchronization with a diurnal motion, a latitude rotation motion, and a rotation frame motion of the fixed star projection globe to prevent a projected position of a planet from deviating with respect to a projected position of a fixed star. Thus, the unnaturalness in star-field reproduction which is a disadvantage in the prior art can be avoided.
2) For the same reason, the eclipse of light during the projection is not produced.
3) Regardless of the adoption of the aforementioned construction, without relying on the driving scheme of each planet projector by the use of a gear train, the present invention achieves success in the adoption of a scheme of driving each of the planet projectors under biaxial control on the basis of calculated values. Hence, the present invention allows the projection in a short time even in the reproduction of a long-time movement of a planet. Further, high-accuracy reproduction is permitted because of an easy position correction by calculation.
4) The projection of the movement of planets is not controlled by a main computer directing the control of the entire planetarium as in the case of the prior art, but is controlled by a planet-movement operation unit isolated from the main computer. This configuration allows the dispersion of the load of processing and the control for the planet projection system even when trouble occurs in the main computer.